Radiosynthesis and Evaluation of Novel Cholesterol 24-Hydroxylase Positron Emission Tomography Tracers

ABSTRACT Cholesterol 24-hydroxylase (CH24H or CYP46A1) is a pivotal enzyme in brain cholesterol metabolism and has emerged as a therapeutic and imaging target in neurodegenerative disorders. Although [ 18 F]Cholestify ([ 18 F]CHL-2205) has shown promise as a positron emission tomography (PET) tracer for imaging of CYP46A1, the impact of cyclopropyl moiety conformation on binding and imaging performance remains unexplored. Here, we report the rational design and preliminary evaluation of novel CYP46A1 PET tracers, in which the left-side cyclopropyl group was modified into bridged, spirocyclic, and fused bicyclic architectures to probe steric and conformational effects. All compounds 9 – 11 exhibited high CYP46A1 affinity (IC 50 = 0.19–0.28 nM). Radiosynthesis of [ 18 F] 9 – 11 was achieved via copper-mediated [ 18 F]fluorination, providing practical non-decay-corrected radiochemical yields of 10–34% with excellent radiochemical purity (>98%). In vitro autoradiography in rat brain sections demonstrated specific and regionally selective binding, comparable to that observed for [ 18 F]CHL-2205. These cyclopropyl-derived scaffolds establish a scaffold-driven strategy for PET tracer development, providing a robust framework for further structure–activity relationship studies and the rational optimization of CYP46A1 PET tracers.